Haleh Karbala Ali , Christopher J. Bean

The aim of this study is to develop methods for directly detecting energetic groundwater flow in sub-surface conduits through passive seismic applications, by detecting the small ground vibrations (seismic microtremor) that flowing water in the sub-surface may generate. This is in contrast to the current ‘traditional’ approach of attempting to actively image the conduits using geophysical and other methods, in order to determine the geometry of flow paths. The imagery of conduits in karst is a very difficult problem and determining if they contain flowing structures is also a very significant challenge using traditional methods, which is the motivation for developing a new approach to the problem. We observed that subterranean flow-related micro-tremor in karst also appears as persistent frequency bands on the spectrograms that vary with time and seismic station location with respect to the conduit. This persistent frequency is different than the soil resonating frequency and relates to the subterranean water flow in the conduits. Application of an Amplitude Location Method (ALM) to the linear profiles clearly delineated the conduit as the source of the micro-tremor in experiments conducted in Ireland. We also discovered a secondary (previously unknown) tributary at one site which demonstrates that this method has the potential to delineate complex subsurface flow structures. We applied the Amplitude Location Method (ALM) to active sledgehammer shots successfully locating the hammer shots. This validates the approach that we are taking and gives confidence in both the concepts behind and implementation of the methodology.